The invention concerns a process for the non-destructive measurement of material accumulations or coating thicknesses on materials with a hollow or open cross section consisting of sheet, strip, or profiled materials, and also concerns devices for the implementation of the measuring process.
For the nondestructive measurement of materials with an open cross section, such as sheet, strips, or the like, nondestructive measuring processes are known that are based on the absorption of X-rays or which function with the radiation from radioactive sources. These processes have the disadvantage that endangerment of the operating personnel is possible, in particular, in the case of damage to the measuring apparatus, and they therefore require particularly costly precautionary measures that must satisfy the legal restrictions.
Also known for the nondestructive measurement of materials with an open cross section are processes that are based on the principle of the mechanical displacement pickup, or the principle of magnetic induction or eddy currents. These processes require counterpressure of the material under test against a substrate by means of the measurement probe; therefore, they are less suitable for the measurement of materials under test that are plastic at the time of measurement.
In the measurement of materials with a hollow cross section, such as hollow profiles, parasons, or such, with the aid of conventional processes, particularly in the case of small cross sections, there is a falsification of the measurement result due to the presence of layers adjacent to the layer to be measured such as opposing layers. The arrangement of a second measuring probe in the interior of the profile for the avoidance of this effect is in most cases not possible for mechanical reasons.